Cold light source



Jan. 14, 1936. J. B. DAVIS ET AL COLD LIGHT SOURCE Filed Sept. 24, 1932Patented Jan. 14, 1936 s PATENT OFFICE COLD LIGHT SOURCE John BurgessDavis, Keyport', N. 1., and James L.

Simpson, New York, N. Y., assignors to Columbia Phonograph Company,Inc., Bridgeport, Conn., a corporation of New York Application September24; 1932, Serial No. 634,643

'This invention relates to new and useful im- .-provements in lamps andhas relation to a lamp particularly adapted for use in televisionapparatus. 5 An object of the invention is to provide a lamp which willgive intense illumination.

Another object is to provide a lamp as stated and including meanswhereby the illumination from the lamp may be concentrated or confined10 so as to form a small intense-spot of light.

A further object is to provide a lamp as stated and which is soconstructed asto "deliver a cold li ht.

Other objects and advantages will become ap- ;5 .parent from aconsideration of the following detailed description taken in connectionwith the accompanying drawing wherein satisfactory embodiments of theinvention are shown.- However, it will be understood that the inventionis m not limited to the details disclosed but includes all suchvariations and modifications as fall within the spiritof the inventionand the scope of the appended claim.

.' In the drawing: v

151 Fig. 1 is a view partly in sectionand partly in side elevationshowing a complete lamp constructed in accordance with the invention;

1 l ig. 2 is a somewhat similar Mew showing a slightly modifiedconstruction; y no Fig. 3 is a detail view showi g a slightlymodifiedparrangement of fused silica cone arrangement which may beemployed; and

4 Fig. 4 is a detail view of the coil.

vIt is well known that gas at low pressure in an 865 enclosed chamberwhen introduced into a radio frequency field may be made to ionize andresonate so as to emit light fiiciently in the visible and ultra-violetfrequencies. The vapor of meronly has been demonstrated to beparticularly.

so efilcient when used in this way, emitting about five candle-power forevery watt of electrical energy dissipated in the vapor.

Referring now to the drawing and at first particularly to Fig. 1, themercury is enclosed in a I 45 highly evacuated quartz bulb 5 including abody portion the walls of which are tapered as shown and at one endthebody 6 may include a hollow bulb like portion 1 while at its other endthe body is enlarged 'as at 8 and closed as by a wall so or window 9.Leading from the lower side of the enlarged portion 8 of the bulb is atubular portion in communicating at its lower end with a hollow bulb i lwhich bulb forms a reservoir and any contain mercury as indicated at It.so 'niceflectivendof thelamp orbulb lisrepresented by the fiat wall orwindow 9 which may be optically ground. A high frequency coil I3 islocated closely adjacent this wall or surface and the energy dissipatedis sufiicient' to evaporate a portion of the mercury and eneigize thevapor. 5 To facilitate this operation the coil may be carried about thechamber or reservoir H as indicated at ll. Any excess of mercury willcondense in the chamber or bulb-like portion i and the intensity of thevarying magnetic field in the 1d coil is suchas to maintain asuificiently high vapor pressure in the forward or enlarged portion 8 ofthe body 5.

When the body 6 is introduced into a magnetic field the energydissipated in the body is much 16 'more than suflicient to excite themercury vapor in the space just adjacent the flat surface l.Consequently with such an arrangement a large portion of the lightproduced or all the energy consumed, is not in a form readily availablefor so use. with the bulb entirely withdrawn from the coil and with thecoil in close relation to the region adjacent the window or wall 8 theregion in contact with said wall becomes more intensely excited-than ifsaid wall or said region were as within the coil.

The coil l3 (see particularly Fig. 4) is in the form of a pancake coilarranged closely adjacent the end or wall 9 of the bulb 5 and the innerturn of the coil is just large enough for the bulb to 30.

pass through. Obviously, the coil may have a greater or lesser number ofturns than is shown in the accompanying drawing. Further, the bulb llmay be heated either by stray field from the coil It or by continuing anadditional turn of 5 the coil about the bulb as at ll.

The rapid movement of electrons and ions in the bulb 5 may prove asource of diiilculty in the higher candle power lamps in that thebombardment of the quartz or silica surface of the bulb 40 by the ionsand electrons results in the generation of heat. This heat is enough tobring the silica to a bright red glow. In order to reduce the heatingeflect of this bombardment we have arranged for cooling of the quartzsurface. 45

To this end a water jacket l5, which is preferably of quartz fused tothe body, is disposed chamber serves to equalize the water pressure whenthe water expands due to heating.

If desired, and to decrease the energy absorbed by the cooling water,water of the grade known as electrolytic conductivity water in a closedsystem wherein the water circulates primarily because of its own'variation in density may be used. This conductivity water and in factthe water used in the system irrespective of the character of the watermay be cooled as by enclosing the coil I I in a housing II andconstantly passing water through said housing from any suitable source.

When, to a large extent, the ionization is conlined to the forwardregion of the bulb as the portion I in Fig. 1 a relatively large coolingchamber I! may be used and thus the necessity for conductivity water maybe eliminated. This is to the fact that the stray field will not, ofitself, be suiiicient to cause much heating of the water due to eddycurrents.

In the device thus far described it will be appreciated that a highcandle power is obtained at the end or window 0. In television,particularly, it is important to have not only high total candle powerbut high candle power intensity. For good scanning it is advisable tohave a point source of light of high intensity. To this end a solid conell of transparent or translucent refractory material which does notconduct electricity, such as fused quartz, fused silica or the like, isemployed with the bulb I.

The cone 2! may be formed with the bulb I or may be formed separatetherefrom and sealed on the window or wall of the chamber or enlargedportion 8 of the bulb and the light from said wall of the bulb is thusconcentrated down to a window 22 whose surface is optically smooth andwhose diameter does not exceed of an inch. When the cone is formed mtefrom the bulb and sealed on the window I the large end of the cone aswell as the window is ground optically smooth. As at prwent determinedthe length of the cone must be at least four or five times the diameterof the window or wall I. The slope of the coneissuchasto insurethatmostof the light emanating from the window I strikes the cone surface atless than the critical angle of reflection. In this way almost 100%concentration of light is attained.

Light emanating from the window 22 spreads over a completehemi-spherical surface and in order to pick up this light andconcentrate it we have the choice either of lenses or of mirrors. Iflenses corrected for spherical aberration are used, evidently a largeportion of the total 180' sphericalanglewillnotbeintercephd. Ifparabolicmirrors are used for pick-up it h evident tlnt the radio frequency coilwill cast a large shadow in the beam reflected from the surface of suchmirror.

.To carry the light away from the coil or to a point where the lightreflected by a. parabolic mirror will not be partly intercepted by thecoil a cone 24 such as shown in Fig. 3 may be employed. In this figurethe end of the cone is turned downwardly as at 25 and the small windowis indicated at 20. Of course, if desired, the extended portionrepresented at 28 may be in the form of a suitably tapered rod sealed toan end surface of the cone and the rod may be bent in the desiredmanner.

In Fig. 2 is shown a slightly modified arrangement of lamp. In thisfigure all of the parts are of the same construction and bear the samereference characters as the parts shown in Fig. 1 with the exceptionthat a tube 21 is provided connecting the bulb or chamber 1 with thereservoir I i. whereby mercury condensed in the bulb l is continuouslyreturned to the reservoir, the said mercury returning through the tube21. If desired, the cone 24 of Fig. 3 may, of course, be applied to alamp having a body structure including tube 21 as disclosed in Fig. 2.Also, it will be understood that the complete cooling system as shown inFig. 1 may be applied to the arrangement shown in Fig. 2, but a part ofthe cooling system being shown in that figure to prevent needlessrepetition.

It will now be understood that with the lamp as described with the coilll located closely adjacent the window or end wall 9 the most intenseionization will take place adJacent said wall with the result that theenergy expended is more nearly all consumed in useful work. Further, itwill be understood that the cone need not be formed with the body 8 butmay be formed separate therefrom and sealed thereto in position over thewall or window 8. Also, the inclined walls of the body I serve to returnthe condensed mercury to the reservoir.

Having thus described the invention, what is claimed is:

A mercury vapor induction lamp comprising an evacuated container, saidcontainer having a discharge region and mercury storage region, aquantity of mercury in said storage region, a water cooling jacket forsaid discharge region, and high frequency means disposed in proximitytosaid storage and discharge regionsfor providing a supply of mercuryvapor and maintaining a discharge therethrough.

JAMEL. N. I

J. Bumms DAVIS.

wante

